The invention relates to a valve seal of a valve assembly.
As discussed in U.S. Pat. No. 5,056,758 to Bramblet, it has been known to use a "fire-resistant" packing including a first set of packing rings of elastomeric material and a second set of packing rings of graphite composition to provide a valve stem seal at both normal operating temperature conditions and abnormally high temperature conditions.
As discussed in U.S. Pat. No. 5,326,074 to Spock, Jr. et al., in valves designed for use in environments subject to thermal cycling, it has been known to dimension a sealing cavity to compensate for thermally induced relative dimensional changes between metallic structural members and sealing materials.